Chemical resistant coatings are designed to protect harmful levels of chemicals in an external environment from penetrating the coated materials and from reaching the objects covered by the protective coated materials.
Chemical resistant coating materials can be coated onto protective clothing to protect wearers in a harsh environment where it may present a potential hazard of exposing an individual to harmful or noxious chemicals. Traditionally, protective clothing has been designed to trade protection for comfort due to material limitations. Those offering more chemical protection were extremely uncomfortable, and those that were of acceptable comfort did not offer acceptable protection. For example, it was known in the art, impermeable materials can exhibit low permeability to harmful chemicals. A good example is the use of butyl rubber as the chemical barrier for making shoes and gloves. Although butyl rubber with sufficient thickness may provide adequate protection from harmful chemicals, it does not allow any water vapor to permeate. Such a material is characterized as non-breathable. Human body's process of heat dissipation normally can be achieved by evaporation of perspiration. Without significant transmission of water vapor, or breathability, prolonged use of non-breathable materials can result in intolerable discomfort due to elevated body temperature and could eventually cause death to a person wearing coverings made from these materials. High levels of sweat moisture generated by the wearer could build up inside the protective covering, followed by heat stress resulting from lack of evaporative cooling. These issues of non-breathable protective covering materials make them only suitable for very short duration usage or limited areas of coverage.
On the contrary, many breathable materials with significantly high water vapor transmission rates, including woven or nonwoven textiles, cannot provide adequate levels of protection against harmful or noxious chemicals. Although they could offer satisfactory comfort, yet they do not provide needed protection. Many research efforts have been made to resolve the trade-off between protection and comfort. For example, it has been known in the art to incorporate absorptive active carbon into textile materials to protect the wearer in a contaminated environment such as described in U.S. Pat. No. 4,510,193 by Blucher et al, U.S. Pat No. 6,571,397 by Williams, and U.S. Pat. No. 6,591,427 by Bennett. Absorptive chemical protective systems work by absorbing hazardous liquids and vapors with sorbents, such as active carbon. Sorbents are limited by a finite capacity to absorb limited quantity of chemicals, and upon sorbents reaches its maximum absorption capacity, protection can no longer be provided. Thus, the available capacity for the adsorption of the chemicals is limited, usually within a few weeks. Moreover, adsorptive systems absorb any chemical, good or bad, present in the atmosphere upon exposure, reducing their available capacity over short period of time. This limits the duration of use and the storage life of such materials.
The limited capacity and indiscriminate absorption characters prompt the necessity of very large quantities of absorptive materials for a chemical protective covering to achieve good levels of protection. It results in very thick heavy barrier systems that have high resistances to heat and moisture transfer, which can impart undesirable physiological heat stresses on the wearer. Thus, absorptive systems are highly restricted by a trade-off between protection and comfort. Additionally, bulky and heavy coverings are also very undesirable for the packaging, storage, handling, and transportation of these materials.
A preferred approach to creating chemical protective coverings that provides satisfactory comfort and protection uses a continuous polymer layer that allows the transmission of moisture vapor that facilitates perspiration, while strictly restricting the passage of undesired noxious chemicals. It would be desirable for a polymer material to have high selective permeability towards water vapor relative to harmful chemicals. Particularly for chemical protective clothing, the permeability to water vapor should be significantly higher than the permeability to noxious or harmful chemicals. This can be the fundamental for good protective coverings that will be both highly comfortable and protective. Since these materials do not rely on absorption of chemicals, they are not limited by the absorption systems. Comparatively, these highly selective permeable materials can be made much thinner and lighter in weight. It significantly improves the heavy, bulky, and sweaty characteristics of absorptive system.
There have been attempts to provide chemical protective coverings that are somewhat comfortable yet provide limited protection from noxious chemicals. For example, films using cellulose-based polymers were taught in U.S. Pat. No. 5,743,775 by Baurmeister and U.S. Pat. No. 6,792,625 by Hexels, and films made of polyimide polymers were taught in U.S. Pat. No. 5,824,405 by White. Films using polyalkylenimine based material were also taught in U.S. Pat. No. 5,391,426 by Wu and in U.S. Pat. No. 6,395,383 by Maples. However, the inherent properties of all these polymeric material systems can be stiff, noisy and fragile in response to body movement, which made these systems not fit for use in protective clothing applications.
U.S. Pat. No. 4,824,916, teaches water-insoluble, crosslinked sulfonated aromatic polyamide and polyurea materials. U.S. Pat. No. 4,273,878 teaches polyamine-crosslinked anion exchanged resins produced by reacting polychloromethylstyrene with polyamine. These aromatic ionomers can also be too stiff, rigid, and noisy not fit to flexible protective clothing applications.
U.S. Pat. No. 4,238,378 teaches polyurethane cationic dispersion containing polyalkylene oxide polyethers. U.S. Pat. No. 5,153,297 teaches water-dispersible electrolyte-stable polyetherester-modified polyurethane ionomers. U.S. Pat. No. 5,629,402 teaches polyurethane containing ionic groups and polyethylene oxide units. These polyurethane ionomers are flexible and breathable, but lack of needed chemical resistance against noxious chemicals. Therefore, they are also not suitable for chemical resistant protective clothing applications.
U.S. Pat. Nos. 4,469,744 and 4,515,761 and 4,518,650 issued to E. I. Du Pont de Nemours and Company taught protective garments made of materials based on fluorinated ion exchange polymer which are highly permeable to water vapor but slightly impermeable to certain organic chemicals. However, fluorinated ion exchange polymers are too expensive to produce, retarding the use of these materials in protective clothing applications.
U.S. Pat. Nos. 6,579,948 and 7,307,127 taught the use of self-assembled sulfonated block copolymer of isobutylene and sulfonated polystyrene as semi-permeable membrane. These membranes are flexible; however, these membranes do not seem to have sufficient selective permeability against noxious chemicals.
Therefore, it is very desirable to find materials not only having high selective permeability toward water vapor relative to noxious or harmful chemicals but also having durable and flexible mechanical properties to fit actual clothing usage applications. Such flexible materials would serve to simultaneously reduce the exposure of a wearer to noxious chemicals and allow a high rate of moisture vapor transmission under conditions of normal use and care, and that are economical affordable for use in protective garments. These materials should also maintain protective properties upon exposure to high temperatures, laundry by water, and chemicals and environmental contaminants such as fuels, lubricants, and oils.